Binding to a datasource using RxDatasources

Question

I have a list of models that I fetch from a server, and basically I get array of these:

struct ContactModel: Codable, Equatable {
static func == (lhs: ContactModel, rhs: ContactModel) -> Bool {
    return lhs.name == rhs.name &&
    lhs.avatar == rhs.avatar &&
    lhs.job == rhs.job &&
    lhs.follow == rhs.follow
}

let id: Int
let name: String
let avatar:String?
let job: JobModel?
let follow:Bool

enum CodingKeys: String, CodingKey {
    case id, name, avatar, job, follow
}

}

So I want to show a list of contacts in my tableview.

Now I have this struct as well which is wrapper around this model:

struct ContactCellModel : Equatable, IdentifiableType {
    
    static func == (lhs: ContactCellModel, rhs: ContactCellModel) -> Bool {
        
        return lhs.model == rhs.model
    }
    
    var identity: Int {
        return model.id
    }
    
    var model: ContactModel
    var cellIdentifier = ContactTableViewCell.identifier
}

What I am trying to do, is to create datasource using RxDatasources, and bind to it, like this(ContactsViewController.swift):

let dataSource = RxTableViewSectionedAnimatedDataSource<ContactsSectionModel>(
            configureCell: { dataSource, tableView, indexPath, item in
                if let cell = tableView.dequeueReusableCell(withIdentifier: item.cellIdentifier, for: indexPath) as? BaseTableViewCell{
                    cell.setup(data: item.model)
                    return cell
                }
                
                return UITableViewCell()
                
            })

but I am not sure what I should do right after. I tried something like this:

Observable.combineLatest(contactsViewModel.output.contacts, self.contactViewModel.changedStatusForContact)
            .map{ (allContacts, changedContact) -> ContactsSectionModel in
               
               //what should I return here?
            }.bind(to: dataSource)

I use combineLatest, cause I have one more observable (self.contactViewModel.changedStatusForContact) that notifies when certain contact has been changed (this happens when you tap a certain button on a contact cell).

So what should I return from .map above in order to successfully bind to previously created dataSource?

Answer 1

You have to replace the contacts that have changed; all the contacts that were changed, but you can't do that because you aren't tracking all of them, only the most recent one. So you can't do it in a map. You need to use scan instead.

I made a lot of assumptions about code you didn't post, so the below is a compilable example. If your types are different, then you will have to make some changes:

func example(contacts: Observable<[ContactModel]>, changedStatusForContact: Observable<ContactModel>, tableView: UITableView, disposeBag: DisposeBag) {
    let dataSource = RxTableViewSectionedAnimatedDataSource<ContactsSectionModel>(
        configureCell: { dataSource, tableView, indexPath, item in
            if let cell = tableView.dequeueReusableCell(withIdentifier: item.cellIdentifier, for: indexPath) as? BaseTableViewCell {
                cell.setup(data: item.model)
                return cell
            }
            return UITableViewCell() // this is quite dangerious. Better would be to crash IMO.

        })

    let contactsSectionModels = Observable.combineLatest(contacts, changedStatusForContact) {
        (original: $0, changed: $1)
    }
        .scan([ContactsSectionModel]()) { state, updates in
            // `state` is the last array handed to the table view.
            // `updates` contains the values from the combineLatest above.
            var contactModels = state.flatMap { $0.items.map { $0.model } }
            // get all the contactModels out of the state.
            if contactModels.isEmpty {
                contactModels = updates.original
            }
            // if there aren't any, then update with the values coming from `contacts`
            else {
                guard let index = contactModels
                        .firstIndex(where: { $0.id == updates.changed.id })
                else { return state }
                contactModels[index] = updates.changed
            }
            // otherwise find the index of the contact that changed.
            // and update the array with the changed contact.
            return [ContactsSectionModel(
                model: "",
                items: updates.original
                    .map { ContactCellModel(model: $0) }
            )]
            // rebuild the section model and return it.
        }

    contactsSectionModels
        .bind(to: tableView.rx.items(dataSource: dataSource))
        .disposed(by: disposeBag)
}

typealias ContactsSectionModel = AnimatableSectionModel<String, ContactCellModel>

struct ContactCellModel: Equatable, IdentifiableType {
    var identity: Int { model.id }
    let model: ContactModel
    let cellIdentifier = ContactTableViewCell.identifier
}

struct ContactModel: Equatable {
    let id: Int
    let name: String
    let avatar: String?
    let job: JobModel?
    let follow: Bool
}

struct JobModel: Equatable { }

class BaseTableViewCell: UITableViewCell {
    func setup(data: ContactModel) { }
}

class ContactTableViewCell: BaseTableViewCell {
    static let identifier = "Cell"
}